Low emission direct fired process air heating

ABSTRACT

A system and method for heating process air is disclosed. Low NOx burners are provided with low temperature combustion air, e.g., less than about 0° C., and fuel at varying amounts to maintain a desired balance between low NO 2  and low CO emissions. The amount of combustion air and the amount of fuel may be adjusted to achieve desired low NO 2  and low CO via a feedback control system.

PRIORITY CLAIM

This application claims priority to U.S. Provisional Application No. 63/035,743, filed Jun. 6, 2020. The entirety of this application is incorporated herein by reference.

FIELD OF INVENTION

The present invention relates to the field of process air heating and, in particular, low emission direct fired ventilation air heating.

BACKGROUND

Ordinances, regulations, and/or laws in a jurisdiction may regulate emissions from heaters and/or air quality of ventilation air in a closed space. For example, some laws may limit the amount of carbon monoxide (CO), carbon dioxide (CO₂), nitrogen dioxide (NO₂), nitrogen monoxide (NO), sulfur dioxide (SO₂), and other pollutants that may be included in ventilation air and/or emissions from burners emitted into the atmosphere or ambient air. In some instances, electric heaters, indirect fired heaters, and direct fired heaters may be used to heat process air for ventilation (e.g., to heat ventilation air). Electric heaters may be expensive to operate as compared to indirect fired heaters and direct fired heaters, but indirect and direct fired heater burn fuel (e.g., ethane, methane, propane, natural gas, etc.) which may generate pollutants.

Specifically, indirect fired heaters pass combustion products (e.g., fuel-heated air) through a heat exchanger to indirectly heat the process air. The heat exchanger prevents the ventilation air from mixing with the combustion products and, thus, the emissions from the burner do not mix with the process air. However, indirect heaters may also be expensive to install and less efficient as compared to direct fired heaters. Direct fired heaters burn fuels to directly heat process air. Thus, combustion products from the burners of the direct fired heaters are mixed with the process air. The direct fired heaters may be less expensive to install and operate as compared to electric heaters and indirect fired heaters, but the emissions from the burners may be above the air quality/emissions limits for processes set by laws and/or regulations of jurisdictions.

In view of at least the aforementioned issues, improved ventilation heating is desired. For example, a direct fired heater that can heat process air without exceeding jurisdictional air quality/emission ordinances, regulations, and/or laws may be desired.

SUMMARY

The present invention relates to a system and method for a direct fired process air heating with low emissions. In accordance with at least one embodiment of the present invention, the direct fired process air heater includes a low emissions burner assembly, a combustion air fan, or blower assembly, a process fan and one or more controllers for controlling the process fan, blower assembly, and a flow of fuel to limit burner emissions. The present application also relates to improving emissions and efficiency of direct fired burners by chilling input air into the direct fired burners.

BRIEF DESCRIPTION OF THE DRAWINGS

To complete the description and in order to provide for a better understanding of the present invention, a set of drawings is provided. The drawings form an integral part of the description and illustrate an embodiment of the present invention, which should not be interpreted as restricting the scope of the invention, but just as an example of how the invention can be carried out. The drawings comprise the following figures:

FIG. 1 is a diagram depicting a general layout of a mine, according to an embodiment.

FIG. 2 is a top view of a direct fired heating process air system, according to an embodiment.

FIG. 3 is a side view of the direct fired heating process air system of FIG. 2.

FIG. 4A is a perspective view of a low NOx burner assembly, according to an embodiment.

FIG. 4B is a top view of the low NOx burner assembly of FIG. 4A.

FIG. 5 is a block diagram illustrating the air flows and control signal inputs/outputs of each component of a direct fired heating process air system, according to an embodiment.

DETAILED DESCRIPTION

The following description is not to be taken in a limiting sense but is given solely for the purpose of describing the broad principles of the invention. Embodiments of the invention will be described by way of example, with reference to the above-mentioned drawings showing elements and results according to the present invention.

Heaters with low NOx burners are generally used in high temperature industrial processes to preheat process air with low NOx (e.g., NO, NO₂ etc.) and/or CO emissions. That is, high temperature air, e.g., greater than 20° C., is supplied to the low NOx burner to combust a fuel. The air supplied to the burner may also be pre-heated to improve thermal efficiency of the heating system. In many applications, this improved thermal efficiency is of the utmost importance. Additionally, low NOx burners are generally used for high temperature industrial heating and not for ventilation heating.

However, in embodiments described herein, low NOx burners are supplied with low temperature air, e.g., less than about 5° C., less than 2° C., or less than 0° C., and fuel, e.g., natural gas, methane, propane, etc., at varying amounts to maintain a desired balance between low NO₂ and low CO emissions. Using a low NOx burner with low temperature combustion air may contradict industry standards; however, it was discovered that the low temperature combustion air may maintain a desired level of both NO₂ and CO in real-time. Notably, in at least mine ventilation scenarios, the specific characteristics of the mine and ventilation system allow the burners to utilize cold air, e.g., below 5° C. For example, in a mine, thermal efficiencies that are common for combustion in other industrial settings—often achieved by pre-heating air for a burner—are not necessary since all heat goes into ventilation. Moreover, other justifications for pre-heating air for a burner, such as to dry fuel, may be inapplicable to mine ventilation.

That said, generally, to maintain low NOx emissions in a low NOx burner, a combustion air blower, or combustion air fan, supplies a set percentage of excess air based on volume (e.g., an amount of air above the stoichiometric requirement for complete combustion) or combustion air to the burner to maintain a flame temperature and stability. For example, excess air is commonly set to less than 15% based on volume. As the flame temperature decreases, NOx decreases, but CO increases. Maintaining a desired balance between emission amounts of NOx and CO may be achieved by setting the flame temperature of the burner. A supply of fuel to the burner may be varied to achieve a desired amount of heating.

With the system and method presented herein, the temperature and/or amount of combustion air and/or the amount of fuel provided to a burner is adjusted in real-time via a feedback control system to achieve desired low NO₂ and low CO emissions while heating process air from less than 2° C. to up to 8° C. That is, inlet process air may be have a temperature of less than 5° C., less than 2° C. and/or less than 0° C. and may be heated to up 8° C., 5° C. or 3° C. (or any temperature above freezing). In some implementations, the combustion air may be provided from ambient air or the atmosphere. The ambient air may be near or below freezing temperatures, e.g., at or less than 5° C., less than 2° C., or less than 0° C. Additionally or alternatively, the combustion air may be pre-cooled, or chilled, to near freezing or below freezing temperatures via a chiller, or a refrigeration unit. Additionally, or alternatively, a percentage of excess air based on volume supplied to the burner may be 15% or higher. That is, the percentage of excess air may be greater than 15%, greater than 20%, greater than 50%, greater than 100%. Overall, setting combustion air temperature at or below freezing and/or setting the percentage of excess air above 15% may facilitate maintaining a flame temperature of the burner at a desired level that provides desired emissions.

In at least some implementations, the burner may discharge combustion products into an inlet of a process fan. That is, process air and combustion products from the burner may be drawn into the inlet of the process fan. The combustion products, or emissions, from the burner may mix with the process air, thereby heating the process air. The process air may be used as ventilation, for example, to ventilate underground mines. In a mine, the ventilation air circulates to provide fresh air for miners to breathe. The ventilation air enters the mine via a bore extending from the surface. Supply lines (e.g., hoses transporting water, fuel, hydraulic fluid, and/or other fluids) may be provided in the bore to supply fluids to equipment in the mine. When the surface temperature of the air drops below a threshold temperature, the ventilation air may cause the supply lines to freeze. The frozen supply lines prevent the desired fluids from reaching desired equipment in the mine. Ventilation air can be heated prior to entering the mine bore to prevent the supply lines from freezing.

FIG. 1 represents a general mine ventilation layout with airflow control equipment according to example. As shown in FIG. 1, a mine may generally include the following elements: one or more exhaust fans 1; one or more intake fans 2; one or more downcast shafts 3; one or more upcast shafts 4; mine levels 5, 6, 7 having one or more extraction zones 10, 11, 12, 13, 14; one or more auxiliary fans 15, 16, 17, 18, 19; and ducting. The mine may also include one or more service areas 29 with an associated auxiliary fan 30. The mine layout provided in FIG. 1 is for example purposes only and embodiments are not limited thereto.

Generally, the one or more intake fans 2 provide air from the surface atmosphere to the underground infrastructure via one or more downcast shafts 3. The fan speed may be controlled by a local controller or by a basic control system with surface HMI (Human Machine Interface). The control system may also include startup and shutdown sequences and protection interlocks.

The one or more downcast shafts 3 provide fresh air and allow hoses to supply fluid to working levels where production occurs on one or more extraction zones 10, 11, 12, 13, 14 off each level 5, 6, 7. Ramps or access shafts 8, 9 with or without access doors may divert some air from each levels to other levels. Ramps 8, 9 provide a route for equipment to move from one level to another. Ore and waste material may be extracted from the production zones by machinery and may be dropped in or passes down to lower levels to be crushed and brought back to the surface by conveyors in shafts elements 26, 27. In some implementations, the machinery may be fueled by diesel fuel, natural gas, or other fuels.

Air may be forced from each level to the ore extraction zones or service areas 10, 11, 29, 12, 13, 14 by auxiliary fans 15, 16, 30, 17, 18, 19 and ducting connected to the fans 15, 16, 30, 17, 18, 19. Like the surface fans, the auxiliary fans speed may be manually or automatically controlled by a local controller or by a basic control system with surface Human Machine Interface (HMI). The diesel particulate emission contaminated air from the ore extraction zones comes back to the level via the ore extraction. Contaminated air may flow to the one or more upcast shafts 4 through fixed opening bulkheads or bulkheads with variable air flow regulators 23, 24, 25. The air flow regulators position is manually or automatically controlled by a local controller or by a basic control system with surface HMI. In some modern implementations, air flow measurement stations 20, 21, 22 may be installed at the bulkheads.

If the one or more surface fans 2 exceed capacity, lower levels may have additional booster fans 28 to enhance ventilation pressure. The fan speed of any additional booster fans 28 may be manually or automatically controlled by a local controller or by a basic control system with surface HMI. The control system usually also includes startup and shutdown sequences and protection interlocks.

The one or more exhaust fans 1 draw air from one or more upcast shafts 4 out to the surface atmosphere. The one or more fans' speed may be manually or automatically controlled by a local controller or by a basic control system with surface HMI. The control system usually also includes startup and shutdown sequences and protection interlocks.

Now referring to FIGS. 2 and 3, reference is made to a direct fired heating process air system 200, according an embodiment. FIG. 2 illustrates a top view of the direct fired heating process air system 200. FIG. 3 illustrates a side view of the direct fired heating process air system 200. The system 200 includes two air ducts 204, two fans 210 each driven by a corresponding motor 212, two burner assemblies 220, an inlet 230, and an outlet 240. The fans 210, motors 212, burner assemblies 220, and inlet 230 are disposed in an enclosure 250. The enclosure 250 may further include a control room 252 for controlling the system 200. The burner assemblies 220 are disposed between the fans 210 and enclosure inlet 230.

During operation, the fans 210 may draw a flow of process air from the atmosphere through the inlet 230. The process air flows through the inlet and past the burner assemblies 220 to the fan 210. A second flow of air may also be drawn in from the atmosphere to the burner assemblies 220 via a combustion air blower, or combustion air fan, assembly (not shown). Alternatively, a single flow of air could be drawn in (by a combustion air blower assembly or the fan) and split/diverted as needed. Either way, a flow of air through the burner assemblies 220 mixes with fuel and combusts in the burner assemblies 220. The combustion products from the burner assemblies 220 are discharged into and mix with a flow of process air, thus heating the process air. The heated process air enters the fan 210 and is discharged into the duct 204. The heated process air exits the system via the outlet 240.

In some implementations, the outlet 240 may be fluidly coupled to a ventilation bore, or shaft, of a mine. For example, the ventilation bore may be representative of downcast shaft 3 of FIG. 1. However, embodiments are not limited thereto. The system 200 may be applied to any process where low NO₂ and CO emissions may be desirable.

While the system shows two fans 210, two motors 212, and two burner assemblies 220, embodiments are not limited thereto. The system may include any number of fans 210, motors 212, and/or burner assemblies 220. For example, the system may have one fan 210, one motor 212, and/or one burner assembly 220. Further, the system, may have more than two fans 210, two motors 212, and/or two burner assemblies 220.

Referring to FIGS. 4A and 4B, reference is made to a low NOx burner assembly according to an embodiment. FIG. 4A depicts a perspective view of the low NOx burner assembly. FIG. 4B depicts a top view of the low NOx burner assembly. The low NOx burner assembly may be representative of the burner assembly 220 of FIGS. 2 and 3. The low NOx burner assembly 400 includes an air inlet 402, a main gas inlet 404, a mixer 406, a duct plate 408, a pilot 410, manifold assembly 412 and air shroud 414. In some implementations, the low NOx burner may be a Honeywell/Eclipse Minnox burner. The Minnox burner is generally used for high temperature industrial applications and not for ventilation heating at lower temperatures. However, low NO₂ and CO emissions—appropriate for ventilation—may be achieved by adjusting an amount of combustion air to provide 15% or more excess air, and adjusting the temperature of the combustion air to less than 5° C., less than 2° C., or less than 0° C. Thus, the burner assembly 400 may be operated outside its normal operating parameters and/or within a limited range of its normal operating parameters.

During operation, air is driven into the air inlet 402 via a combustion air blower (not shown) and fuel is supplied from a fuel supply to the main gas inlet 404. The fuel and air mixture may flow to the manifold assembly 412 at the base of shroud 414. The mixture is ignited when exiting the manifold assembly 412 and burns as it passes through the shroud 414. An amount of excess air is supplied to the burner 400 to maintain a desired flame temperature within the air shroud 414 and a desired percentage of NO₂ and CO emitted from the shroud 414.

Referring to FIG. 5, a block diagram depicting a flow of air (bold lines) and inputs/outputs of control signals (light lines) from controllers to components of the process system 500 is described. The process system 500 may be representative of the direct fired heating process air system 200 described in reference to FIGS. 2 and 3. As shown in FIG. 5, a flow of combustion air 50, and/or excess air, from an air supply 502, e.g., the atmosphere, ambient, etc., is directed to a pilot burner 520 and a main burner 522 (e.g., burner assembly 220 of FIGS. 2 and 3, and/or low NOx burner of FIGS. 4A and 4B). Additionally, or alternatively, a flow of process air 52 is directed from the air supply 502 to a process fan 510 (e.g., process fan 210 of FIGS. 2 and 3).

Prior to reaching the main burner 522 (and potentially prior to reaching a combustion air blower 524), the flow of combustion air 50 may be directed to a chiller 526 for cooling. The chiller may be or include any components (including mechanical, chemical, electrical, etc. components) that can cool (e.g., reduce the temperature) of a gas (e.g., air) that are now known or developed hereafter. In some implementations, the flow of combustion air 50 may bypass the chiller if the air supply 502 is at a desired temperature. Either way, the flow of combustion air 50 continues to the combustion air blower 524. The combustion air blower 524 accelerates the flow to the main burner 522 and pilot burner 520. The combustion air blower 524 speed may be controlled or adjusted to control or vary the volume of combustion air 50 flowing through the burner 522. Fuel 60 from a valve train 528 mixes with the combustion air 50 at the pilot burner 520 and main burner 522. The burners 520, 522 combust the mixture. The combustion products 56 are then discharged from the burners 520, 522 into the flow of process air 52, mixing with and heating the process air 52 to form a heated flow 52′. The heated flow of process air 52′ then enters the process fan 510 and is discharged to a post heating process 590 (e.g., ventilation shaft of a mine).

During this flow process, operations controls 530 (e.g., a controller, CPU, processor, etc.) can adjust the amount of air 50, 52 and amount of fuel 60 flowing through the system 500 based on feedback from components and sensors. The sensors may include one or more process air temperature sensors, one or more air speed sensors, one or more pressure sensors, one or more NO₂ sensors, and/or one or more CO sensors. At least some of the sensors (e.g., an NO₂ sensor and a CO sensor) may be disposed downstream of the process fan. Sensors (e.g., temperature and pressure sensors) may also be included at the air supply 502.

Generally, the emissions controls 532 (e.g., a controller, CPU, processor, etc.) may receive signals from the NO₂ sensor and/or the CO sensor. Based on the received signals, the emissions controls 532 may transmit instructions to the operations controls 530 and/or the chiller 526. The process fan 510, combustion air blower 524, chiller 526, burners 520, 522, and valve train 528 may also provide feedback to the operations controls 530. For example, during operation, the operations controls 530 may monitor the air supply 502 temperature via a temperature sensor. Based on the air supply 502 (e.g., ambient air) temperature, the operations controls 530 may determine whether to cool the combustion air 50 and the amount of fuel 60 to supply to the main burner 522. The amount of fuel 60 supplied to the main burner 522 determines the amount of heat provided to the flow of the process air 52.

As the combustion products 56 from the burner 522 mix with the process air 52 to form a heated flow 52′ that passes through the process fan 510, an NO₂ sensor, a CO sensor, and a temperature sensor (not shown) disposed downstream of the process fan 510 measure the heated flow 52′ (which may be used as ventilation air). The sensors transmit signals indicative of the amount of NO₂ and CO present in heated flow 52′ and the temperature of the heated flow 52′. In some implementations, the signals from the NO₂ and CO sensors are transmitted to the emissions controls 532. The emissions controls 532 may determine an amount or percentage of NO₂ and CO present in the heated flow 52′. While the operations controls 530 and emissions controls 532 are depicted as separate components, they may be combined into a single component, CPU, or processor.

Based on the determined amount of NO₂ and CO, the emissions controls 532 may determine to adjust the chiller 526 and/or adjust the combustion air blower 524 speed. Adjusting the chiller 526 may increase or decrease the temperature of the combustion air 50. Meanwhile, increasing the combustion air blower 524 speed increases amount, or volume, of excess air, while decreasing the combustion air blower 524 speed decreases the amount of excess air at the burner. For example, in response to determining the amount of NO₂ in the process air is too high, the emissions controls 532 may transmit instructions to the operations control 530 to increase the combustion air blower 524 speed to increase excess combustion air 50 and/or adjust the chiller 526 to cool the excess air. In response to determining the amount of CO in the heated flow 52′ is too high, the emissions controls 532 may transmit instructions to the operations controls 530 to decrease the combustion air blower 524 speed to decrease excess air and/or adjust the chiller 526 to adjust the temperature of the excess air provided to the burner. In some implementations, operations controls may control the air blower 524 speed to provide at least 15% excess air, at least 20% excess air, at least 50% excess air, or at rates above higher thresholds. In at least some embodiments, waste heat can also be recovered and utilized elsewhere in the system.

Thus, a desired level of both NO₂ and CO can be maintained in real-time in heating low temperature air using a burner designed for high temperature applications. Moreover, in some embodiments, these emission levels can be maintained despite inefficiencies introduced by a mechanical valve, or other mechanical regulation device, that is often used to control gas flow into a burner. For example, if the system experiences inefficiencies over time (e.g., due to build-up, wearing of fans, etc.), the system may automatically compensate for these inefficiencies because the control is based on real-time sensor data. By comparison, if an orifice valve, or any other component in a system without such controls, degrades over time, the system may be unaware and unable to compensate until the degraded component is serviced. Thus, the techniques presented herein may provide cost savings (since inefficiencies of mechanical devices are automatically compensated) and avoid costs associated with maintaining a mechanical devices over time. Additionally, or alternatively, the techniques presented here may use any flow regulation device.

The operations controls may receive instructions from the emissions controls and signals indicative of supply air 502 temperature and heated process air 52′ (i.e., a heated flow) temperature from the temperature sensors. Based on the received instructions from the emissions controls 532 and the temperature signals, the operations controls 530 may control the combustion air blower 524 speed to adjust the amount of excess air supplied to the main burner 522, control the valve train 528 to adjust the amount of fuel supplied to the main burner 522, control the chiller 526 to adjust the temperature of the combustion air 50 from the air supply 502, and control a process fan 510 speed. Thus, a desired temperature of the process air may be achieved, or maintained. In at least some embodiments, three-dimensional (3D) mapping may be used to correlate the myriad variables tracked by sensors, predict an amount of heating (e.g., by BTUs) needed in the system (e.g., based on ambient temperature and mine air volume) and control the various components of the system of FIG. 5 based on the same.

In at least some embodiments, the operations controls 530 may control the chiller 526 and/or combustion air blower 524 speed of the system in response to received feedback in real-time to achieve NO₂ emissions of 0.2 to 0.027 parts per million (ppm) or even to at or below 0.1 ppm, CO emissions of 1 to 5 ppm, and SO₂ emissions below 0.25 ppm. By controlling the combustion air blower 524 speed based directly on the emission levels, the control system may have a faster response time with less overshoot than conventional systems that simply adjust fuel level with a fixed percentage of excess air. Alternatively, the operations controls 530 may control the chiller 526 and/or the combustion air blower 524 to achieve different emissions levels. As an example, the techniques provided herein may achieve these emissions for a heater with a total heater capacity will be 120 MM BTU/HR at 1.1 MM CFM, with 80:1 turn-down, consisting of two 60 MM BTU/HR sections and utilizing propane fuel.

While the invention has been illustrated and described in detail and with reference to specific embodiments thereof, it is nevertheless not intended to be limited to the details shown, since it will be apparent that various modifications and structural changes may be made therein without departing from the scope of the inventions and within the scope and range of equivalents of the claims. In addition, various features from one of the embodiments may be incorporated into another of the embodiments. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the disclosure as set forth in the following claims.

It is also to be understood that the process heating system described herein, or portions thereof may be fabricated from any suitable material or combination of materials, such as plastic, foamed plastic, wood, cardboard, pressed paper, metal, supple natural or synthetic materials, derivatives thereof, and combinations thereof.

Finally, it is intended that the present invention cover the modifications and variations of this invention that come within the scope of the appended claims and their equivalents. For example, it is to be understood that terms such as “left,” “right,” “top,” “bottom,” “front,” “rear,” “side,” “height,” “length,” “width,” “upper,” “lower,” “interior,” “exterior,” “inner,” “outer” and the like as may be used herein, merely describe points of reference and do not limit the present invention to any particular orientation or configuration. Further, the term “exemplary” is used herein to describe an example or illustration. Any embodiment described herein as exemplary is not to be construed as a preferred or advantageous embodiment, but rather as one example or illustration of a possible embodiment of the invention.

Similarly, when used herein, the term “comprises” and its derivations (such as “comprising”, etc.) should not be understood in an excluding sense, that is, these terms should not be interpreted as excluding the possibility that what is described and defined may include further elements, steps, etc. Meanwhile, when used herein, the term “approximately” and terms of its family (such as “approximate”, etc.) should be understood as indicating values very near to those which accompany the aforementioned term. That is to say, a deviation within reasonable limits from an exact value should be accepted, because a skilled person in the art will understand that such a deviation from the values indicated is inevitable due to measurement inaccuracies, etc. The same applies to the terms “about” and “around” and “substantially”. 

1. A method for controlling emissions for a direct fired ventilation heater comprising: measuring a temperature of process air; determining, at a processor, to heat a flow of the process air in response to the temperature meeting a criteria; discharging a flow of combustion products from a burner into the flow of the process air to produce a heated flow; measuring an emissions level of the heated flow; and adjusting an amount of excess air provided to the burner in response to the emissions level.
 2. The method of claim 1, wherein the burner is a low NOx burner.
 3. The method of claim 2, wherein the criteria is at or below 0 degrees Centigrade.
 4. The method of claim 2, wherein the amount of excess air is an amount of air supplied to the burner above a stoichiometric amount for complete combustion.
 5. The method of claim 4, wherein the amount of excess air is about equal to or greater than 15 percent of a volume of air comprising the stoichiometric amount for complete combustion.
 6. The method of claim 4, further comprising controlling an amount of fuel provided to the burner based on the temperature of the process air.
 7. The method of claim 1, wherein the amount of excess air provided to the burner is adjusted by controlling a speed of a combustion air blower.
 8. The method of claim 7, wherein the speed of the combustion air blower is controlled, by the processor, based on the emissions level of the heated flow.
 9. The method of claim 1, further comprising guiding the heated flow into a ventilation system, wherein the ventilation system is disposed in an underground mine.
 10. The method of claim 1, further comprising maintaining the emissions level of the heated flow to about 0.2 to 0.027 parts per million (ppm) of nitrogen dioxide, 1 to 5 ppm of carbon monoxide, and/or below 0.25 ppm of sulfur dioxide.
 11. The method of claim 1, further comprising cooling a flow of combustion air provided to the burner via a chiller.
 12. A system for controlling emissions for a direct fired ventilation heater comprising: a low NOx burner; a combustion air blower fluidly coupled to the low NOx burner; and a controller having one or more processors configured to: determine a temperature of a flow of process air; initiate the low NOx burner in response to the temperature of the flow of process air meeting a criteria to generate a heated flow; measure an emissions level of the heated flow; adjust a speed of the combustion air blower in response to the emissions level.
 13. The system of claim 12, wherein the criteria is at or below 0 degrees Centigrade.
 14. The system of claim 12, wherein adjusting the speed of the combustion air blower adjusts an amount of excess air provided to the low NOx burner.
 15. The system of claim 14, wherein the amount of excess air is an amount of air supplied to the low NOx burner above a stoichiometric amount for complete combustion.
 16. The system of claim 15, wherein the one or more processors are further configured to maintain the amount of excess air at a level that is about equal to or greater than 15 percent of a volume of air comprising the stoichiometric amount for complete combustion.
 17. The system of claim 12, wherein the one or more processors are further configured to control an amount of fuel provided to the low NOx burner based on the temperature of the flow of process air.
 18. The system of claim 12, further comprising a ventilation fan fluidly coupled to the low NOx burner; and a ventilation system fluidly coupled to the ventilation fan.
 19. The system of claim 12, further comprising a chiller configured to cool a flow of combustion air provided to the low NOx burner.
 20. The system of claim 12, wherein the one or more processors are further configured to maintain the emissions level of the heated flow to about 0.2 to 0.027 parts per million (ppm) of nitrogen dioxide, 1 to 5 ppm of carbon dioxide, and/or below 0.25 ppm of sulfur dioxide. 